In a large mixing bowl combine all the ingredients for the marinade and whisk it nicely. Now carefully fold in tempeh slices and mix gently so that each tempeh piece is well covered with the marinade. Cover and let it rest for 20 minutes
Now, heat a nonstick pan/crepe pan and grease it to avoid sticking. Place each tempeh pieces on the pan with the help of tongs. Let it cook until nice brown in color. Flip the tempeh pieces to the other side and let it cook again until nicely brown.
Warm up the tortilla and place lettuce leaves, sliced tomatoes, onions and tempeh pieces. Squeeze few drops of lemon juice and fold it nicely so it stays strong. Enjoy immediately.